Many vehicles have audio systems that can reproduce sound into the vehicle cabin. The types of audio played into a vehicle cabin can be categorised as background sources and foreground sources. The background sources are typically entertainment-type sources, for example music from an AM/FM radio, an MP3 player or a CD player that may be continually playing in the background. The foreground sources are typically information-type sources for example announcements from a navigation system, a call from a telephone or a beep from a parking aid system that may be output intermittently or less frequently in order to impart information to the driver as required.
The quality of the sound output by an audio system is dependent upon a number of factors including: the quality of the input sound signals; the environment in which the sound is being played; the number of audio channels being simultaneously output; and the type of audio signals being simultaneously output. Modern audio systems use a single equalisation of one or more mixed audio signals to compensate for the factors that degrade the quality of the output audio.
In many current audio systems the single equalisation used by the audio system to process the incoming audio signals uses settings to optimise only the background source. For example, when an audio signal from a background source (for example music from a CD) is being output through a current audio system and it is required to simultaneously also output the audio signal from a foreground source, (for example a beep from a parking aid sensor), the foreground audio signal is mixed with the background audio signal and then the combined signal equalised using an equalisation setting that is characterised for the CD audio. This can be disadvantageous because the equalisation setting for the CD audio signal may not optimise the parking aid beep. Indeed in some instances, not only is the foreground audio not optimised, but the foreground audio signal can in fact be degraded (sometimes to a critical level) by the equalisation that is applied. For example, the parking sensor may issue a beeping signal at a specific frequency to alert the driver to a nearby object in the path of the parking vehicle. The equalisation setting for the background audio may include a filter for the same specific frequency range in order to compensate for the CD audio having an unwanted peak in that specific frequency range. Therefore, when the background audio and foreground audio signals are together subject to the equalisation settings specific to the CD audio signal, the foreground audio may be reduced to an unsatisfactory level or rendered entirely inaudible.
Additionally, current audio systems are limited in the number of audio signals they can output simultaneously and are limited in the number of audio sources they can support. Typically current high-specification audio systems for vehicles may be limited to simultaneously playing three foreground audio signals mixed with one background audio signal. Even in these audio systems, some combinations of background and foreground source audio signal can be hard to hear due to the effects of the background source equalisation being applied to the combined audio signal comprising the background source audio signal and the three con-current foreground source audio signals.
Furthermore, the number of devices that need to issue information signals to a vehicle user is increasing and current audio systems do not meet the demand to simultaneously output high-quality sounds from a variety of audio sources.
In addition, current audio systems are limited to playing only one background audio source at a time. Typically this has been sufficient because a driver of a vehicle would not want to listen to the radio and a CD at the same time. However, demand is increasing for passenger entertainment and some vehicles are now provided with rear seat screens and DVD players for example. Current in-car audio systems do not accommodate a requirement to play more than one background audio sound.
There is a need for an improved audio system that can accommodate the increasing requirements for multiple audio signals to be supported and output at the same time and at high quality.
It is against this background that the present invention has been conceived. Embodiments of the invention seek to provide an improvement in the field of audio systems. The present invention is not limited in its application to vehicles, but has particular application in vehicles due to the increasing number and increasing type of audio signal that a driver and its passengers wish to listen to, for example: radio (digital and/or analogue), CDs, DVDs, MP3 players, mobile telephones, satellite navigation system, traffic announcement devices, and vehicle warning sounds. The invention may be utilised in applications other than in vehicles, for example it is foreseen that the invention may have application in buildings for example houses, where there are also many different types of audio signal and it may be desirable to output all of them through a single audio system. Furthermore it is envisaged that the present invention may find advantageous application in other devices where management and output of multiple audio signals is carried out, for example phones, smart phones, personal and/or tablet computers, games, hand held devices, consoles and home entertainment audio/visual systems.